LED Popping

[rsocor01]

The LED is in a circuit that's applying high gain to a guitar signal - the clicking from the LED is somehow finding it's way into the signal path.

If you keep the LEDs in the same circuit, all you can do is try to minimize the noise. Try placing a capacitor (1 uF) close to the VCC pins in the pic. Also, for a high gain signal circuits a good ground plane would help. Finally, try reducing the current through the LEDs by increasing the value of the current limiting resistors.

I hope that this helps,

Robert

[Jumper]

Perhaps you can fade in and out the LED using a PWM signal. i.e 30 000 Hz . Then you can make a soft on - soft off function that might work. At some frequency you have passed what the ear can hear and the amplifier can amplify.

[Mike, K8LH]

How about muting the amp' for a few milliseconds after detecting a new switch press and during the time you're lighting the LED?

[HankMcSpank]

Thanks guys....keep 'em coming.

Robert - tried all of those!

Jumper - my PWM pin is in use for other things! (& I want to stay with the PIC I'm using - a 16F690)

Mike - the amp on my circuit is already muted (I didn't explain very well - it's the gain in the guitar amp that is high. The guitar signal feeds into my circuit....which I mute when switching - but this source guitar signal is simply 'Y'ed into my circuit.....the original guitar signal proceeds to the guitar amp as normal - it's this signal that's picking up the LED switching lcick from my circuit.

So the path is like thus....


Guitar pickup 'Y'ed off into two .....
1 ----> into my circuit
2 ----> onwards to the amp as normal (clicking heard on high gain settings from switching in my circuit above)

I need a way of ramping up the led slower so there's no sharp current surge (which is what reckon was causing the pop) - PWM would have been perfect, but like I say, I really want to stick with the 16F690. I have some spare pins left, so it's plausible to do some kind of pseudo PWM.

Toying with the idea of an inductor in series with the led (or possibly bringing a cap into play), just to delay the sharp switch on.

I found this site, but the jury is still out that they've got it wired correctly (I'm pretty sure it's wrong!)...

http://www.muzique.com/lab/led.htm

[rsocor01]

Toying with the idea of an inductor in series with the led (or possibly bringing a cap into play), just to delay the sharp switch on.

A cap in parallel with the LED won't work as the current will rush in to the cap trying to charge it, making matters worse. Now, a resistor in series with an inductor would do just fine. Keep in mind the time constant L/R. One L/R time constant is the time required for the current in an inductor to increase to 63.2 percent of the maximum current. This is similar to the RC time constant in a capacitor+resistor circuit.

By playing with the R and L values, you can adjust the delay that you want for the incomming current. I found this very nice picture on the web that ilustrates this point.



http://www.tpub.com/neets/book2/2d.htm

Robert